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A few decades ago the whoopers swan (Cygnus cygnus) was an endangered and rare species in Finland. It only bred in remote lakes and people rarely saw them. The population increase of whooper swans after protection is one of the success stories in Finnish nature conservation. Nowadays the swans can be heard gaggling all around Finland. The whooper swan is a large bird, and it thus consumes a lot of vegetation. Water horsetail (Equisetum fluviatile) is one of its favourites.

The whooper swan population has increased greatly, and their gaggling can be heard widely in Finland.

Certain other species also prefer water horsetails. For example, wigeon (Mareca penelope) broods forage within the horsetail growths searching for emerging invertebrates. A study published earlier this year showed that the water horsetail is disappearing from Finnish and Swedish lakes. The reasons for this pattern are unknown, but one possible explanation could be increased grazing pressure. Whooper swans effectively utilize horsetails, and swan grazing was therefore suspected to be influencing the disappearance of the horsetail. Wigeon populations have concurrently shown a worrying decrease.

A recently published study conducted of 60 Finnish and Swedish lakes utilized vegetation and waterbird data gathered in the early 1990s and in 2016. The study area widely covers the boreal, reaching from southern Sweden to Finnish Lapland. The whooper swan population increased strongly during the study period. Researchers studied whether whooper swans’ grazing on water horsetail is causing the negative trend in the wigeon population. Pair counts were used to indicate waterbird communities, and thus any changes caused during the brood time were not shown.

Whooper swans are grazers that have to consume a great deal of vegetation to survive.

The study showed that whooper swans strongly preferred lakes with horsetails during the 1990s, but this connections is not seen anymore. While the number of swan-occupied lakes has increased, the number of horsetail lakes has decreased dramatically. However, it appears that swans and disappearing horsetails do not associate, because the horsetail has also been from lakes where swans don’t occur. The horsetail has increased in some swan-occupied lakes.

The number of lakes used by wigeon has decreased, but swans are apparently not causing this. Wigeon loss has not been stronger on lakes occupied by swans. Quite the opposite, as wigeons and swans appear to positively correlate. Even though wigeons prefer horsetail lakes, their disappearance is not associated with the horsetail loss occurring in the study lakes, which suggests that wigeons can also utilize other lake types. On the other hand, the researchers note that this study did not considered the critical brood time, when the foraging opportunities among the horsetail growths are especially important. Thus it may still be possible that wigeons are affected by horsetail loss, but this effect only appears during the brood time.

While scientist struggle with short-term funding periods, the curiosity for nature that the general public shows, can unearth mechanisms that can only be found with long-term datasets. The persistent and systematic observations made by nature enthusts enables research about climate change or life history traits over several generations. Both are issues that require long-term research – and a lot of time and effort. Below are some examples of remarkable work done by citizen scientists curious about nature.

16 000 ringed goldeneyes have passed through the hands of a Finnish fireman

Finnish fireman Pentti Runko has collected systematic data of goldeneyes for several scientific studies. After starting his work in 1984, by 2017 Runko has ringed an amazing 16 000 goldeneyes and checked several hundreds of nest boxes every year.

In a recently published study, the authors utilized data concerning 14 000 of these goldeneyes ringed by Runko between the years 1984-2014. Among these goldeneyes were 141 females that were ringed as ducklings and recaptured later in the area. Based on these data it was possible to follow the recruit females’ lives from hatching to breeding. Thus the early life circumstances of these females are known, and the circumstances can be used to study their effects later on in life. In some cases early life circumstances have severe results on subsequent life, for example on breeding performance (duckling video).

The study was able to show deviations between individuals during the first breeding years and how circumstances during early life affected the breeding statistics of these females. Most females began breeding at the age of 2, but 44% delayed the start of breeding. Winter severity of the first two years affected the timing of breeding, but did not affect which year the females began breeding. As a conclusion, it appears that certain traits buffer the effects that the severity of the first weeks have, so the breeding parameters of females are not affected. The research also showed that first-time breeders tend to begin breeding later than the yearly specific averages.

After ringing ducklings get back to the nest box.

The authors of another study used a set of 405 females and their offspring’s ringed by Runko, and found that the females’ condition matters when it comes to breeding success. Older, early-nesting females with good body condition and larger broods were able to produce more female recruits for the local population. The later the females bred, the less recruits they produced. The study also showed that females tend to adjust their breeding according to the ice-out dates of lakes. However, differences were observed between the flexibility of the females. Because early-breeding goldeneyes succeed better, the authors conclude that selection favours early-breeding individuals.

The lives and breeding habits of goldeneye females are closely followed at Maaninka (video).

Climate change effects can also be observed from goldeneye phenology. Runko showed that during the last 30 years goldeneyes have advanced their egg-laying dates by 12 days.

45 years of starling surveys in a farmer’s backyard reveal climate warming

Starlings are becoming scarce in Europe.

The Danish Ornithological Society Journal recently published a study that utilized data gathered by a Danish farmer, who ringed starlings for 45 years. Dairy farmer Peder V. Thellesen ringed ca. 12 000 starlings nesting in 27 nest boxes, and measured their phenology systematically. The data showed that during the study period starlings advanced their egg-laying dates by more than 9 days. This advance was observed in both first and second clutches. The result reflects the increase in April temperatures. Another important observation was that while no change was observed in clutch size and hatching rate, nest box occupancy has fallen dramatically in recent years. Starlings used to be common in Europe, but now they have decreased widely in Europe, also in Denmark. Changes in agricultural land use, especially decreased cattle grazing, are suspected as one example affecting starling populations. Loss of cattle-grazed land means less insect-rich foraging lands for the birds.

A small pond in the Finnish countryside is filled with squeaking, when several goldeneye (Bucephala clangula) and wigeon (Mareca penelope) broods are foraging. Suddenly a goldeneye hen alerts and flies cackling across the pond. The figure of an American mink (Neovison vison) appears on the water surface, which leads to an emergency escape of the duck broods. The American mink is an efficient predator, which does not belong in Finnish nature. Nonetheless it has already occupied the whole country. Alien species in Finland and other countries are a serious threat to birds.

Duck broods escape after a watchful goldeneye female alerts after spotting an American mink.

A fur farming runaway became a nuisance

The American mink is, as its name reveals, an American species, which was brought to North Europe at the beginning of the 20th century. Minks escaped from farms and were successful in Europe. They were also introduced to nature on the Russian side. Rapidly American minks occupied all of Fennoscandia.

The American mink utilizes various wetlands, lakes and archipelagos, where it predates birds and limits their populations. Minks don’t only eat birds, but also their eggs. The American mink is especially harmful in Fennoscandian archipelagos, because birds are not adapted to such predators. Certain bird species, such as the black guillemot (Cepphus grylle), are especially threatened by mink predation. Traditionally Fennoscandia has not had such predators. The European mink (Mustela lutreola), which is now extinct from many of its historical areas, did not occupy the archipelago in the same way as its American cousin does.

The American mink is currently a common wetland species in Fennoscandia.

Raccoon dog ended up on EU’s black list

The raccoon dog (Nyctereutes procyonoides) is an Asian species that was introduced to the European parts of the Soviet Union to be hunted for its fur. From the Soviet the raccoon dogs spread west. Soon raccoon dogs occupied all of Finland, and are now also reaching Sweden. Currently Finnish hunters are working to prevent raccoon dogs from going over the Swedish border. The raccoon dog was recently classified as an invasive alien species by the European Union. One reason for this is its influence on birds.

Raccoon dog destroys an artificial duck nest. Game camera photo.

Research conducted at the Helsinki University shows that raccoon dog density and predation pressure on artificial nests correlates on wetlands. Other studies have found raccoon dogs to destroy both pheasant and duck nests. Thus raccoon dog removal around wetlands is an important way to protect birds.

And then there were no Stephens Island wrens left

A cat named Tibbles carried little birds to a light house yard on an island of New Zealand in the late 1800s. The birds were Stephens Island wrens (Xenicus lyalli). The cat hunted at least 15, after which apparently none were left. Rats and cats might already have killed the wren populations from the other islands. The Stephens Island wren is not the only victim of cats. Australian researchers have counted that domestic cats have killed at least 20 native species. In the USA cats are estimated to kill 3,7 milliard (3.7 billion) birds annually. Most birds are killed by unowned cats. Cats therefore appear to kill more birds than any other anthropogenic cause in the USA. Worldwide cats have killed 33 animal species to extinction.

A cat stalking a duck brood in a wetland. In this case cutting the vegetation saved the brood.

The raccoon is occupying Europe

In addition to the American mink, the raccoon (Procyon lotor) has also arrived in Europe from North America. The raccoon was also brought Europe to be farmed for its fur. This highly adaptable animal has succeeded well in Europe, and is now common for example in Germany and France. The population size in Germany is already evaluated at over a million. Raccoons are spreading north, and are currently settled in Denmark and individuals have also been found in Sweden. Compared to raccoon dogs, raccoons also live successfully in cities. But just like raccoon dogs, raccoons are also well adapted to the wetland environment, and are thus harmful to waterbirds.

Raccoons reproduce effectively, and therefore their extirpation is impossible once a population has been established. This is why efforts need to be focused on stopping the species from spreading. The raccoon is classified as an invasive alien species in the EU, so farming them or having one as a pet is illegal.

Many geese populations in Fennoscandia are increasing rapidly, and geese have become more visible in human-inhabited landscapes. Currently geese utilize agricultural lands and even urban lawns. High geese brood densities have a significant impact on their environments due to increasing grazing pressure.

Greylag geese graze on pastures and hay lands, preferring short vegetation to high ones. Geese grazing also keeps vegetation short. Geese trimming a lawn in Reykjavik, the capital of Iceland.

Geese broods prefer pastures near shores

A newly published Swedish study revealed that greylag geese broods are rather picky when selecting farmland fields for grazing. The most used fields were pasturelands near water. Goslings preferred shorter vegetation, assumingly due to its higher quality and the open landscape views in case of predators. Grazing geese also keep the vegetation short.

Broods tend to prefer grazing areas near shores, from where they can easily reach the safety of water when threatened. Grazing geese broods are suggested to pose a fairly small risk of agricultural conflicts due to their preference for near-shore pastures (instead of crop fields for example). However, extremely high grazing pressure by geese can reduce plant biomass, thus affecting livestock grazing. In arctic areas, such as Greenland and Svalbard, geese grazing is observed to be the reason for decreased hay and decreased seed counts in soil.

In contrast to broods that prefer near-shore areas, non-breeding geese can cause conflicts with agriculture, due to their grazing in crop fields. Non-breeding birds that are able to fly can utilize areas further from water, and according to a Swedish study, they also graze also on crop and vegetable fields in addition to pastures. Large flocks preferred typically open and flat with no or few trees or shrubs.

The two differing patterns shown by broods and adults means that geese managers should consider the two behavioural strategies when planning geese management.

Barnacle geese grazing among Helsinki University research cattle. Breeding geese flocks have e.g. destroyed some the university’s research fields and caused high expenses.

City geese have found Helsinki’s shore lawns

The barnacle goose is a fairly new species in Helsinki. The species tends to breed in remote arctic areas, but after geese were released from the local zoo in the late 1980s, geese began breeding on the islands and islets of the Helsinki archipelago. The released geese are assumed to have returned to breed, and brought their offspring and other geese with them. Since then the goose population has been growing and occupying shore areas from the islands and mainland. Grazing geese are nowadays a visible element in the city of Helsinki, competing over space with citizens.

Geese densities are rather high on Helsinki shore lawns, where non-flying broods gather to graze. In August juvenile birds can move further from the shoreline to feed. The best seashore lawns tempt dozens of broods. In urban areas lawns are usually a nice buffet table for the geese: they typically prefer plant species used in lawns, and mowing sustains fresh vegetation. Compared to natural lawns, urban lawns can be better for broods.

This geese enclosure has very limited plant diversity, but Potentilla species not preferred by geese are flourishing.

However, geese grazing is affecting plant diversity by decreasing it. Few plant species tend to dominate in the grazed areas, while the diversity and coverage of species is more balanced in areas with no geese grazing. Good quality lawns benefit broods, because they don’t need to move long distances while grazing. Geese population growth in the Helsinki area has been refracting after reaching ca. 1300 breeding pairs, and one reason is thought to be the limitation of good feeding habitats for broods. Geese already use almost all possible lawns in Helsinki. During dry summers with poor lawn growth geese may be greatly food-limited, which is reflected in the population size. Thus it seems that the barnacle goose population in Helsinki has reached its carrying capacity.

In the Helsinki archipelago barnacle geese nest commonly on rocky islands and islets, where food availability is highly limited. Well-managed city lawns are thus tempting for the broods.

Methods for preventing geese grazing were measured in Helsinki. One possibility is to use plant species that geese don’t prefer, instead of the current species mix that seems to be especially tempting for geese. Another possibility is to fence off areas were geese are not welcome. Goslings cannot fly, and thus cannot reach fenced areas, and they also avoid areas where they have limited visual contact to water.

This is a mallard (Anas platyrhynchos). It is your basic duck, familiar from park wetlands. A mallard quack is also the classic duck sound.

A wintering mallard flock is quite colourful: males have green heads with yellow beaks and both sexes have blue wing spots.

Age and season affect plumages

But mallards do not always look like those in the picture above. Males do not always have green heads, nor are females always brownish grey. Depending on the season, and the age and genes of an individual, mallards can look a little different. Downy ducklings resemble the ducklings of all other dabbling duck species. However, they rapidly develop species-specific characters, and young drakes for example develop a hint of green on their head even before all the down has disappeared. In the summertime males briefly change into summer (eclipse) plumage that looks like female plumage. Except that a male beak is still yellow.

In addition to normal changes in plumages caused by seasons or growth, weird looking mallards can also be found. Their plumages might be different due to changes in their genes or hormones.

Light female mallard.

Various phenotypes are rather typical among animal species. These variations are common in mallards, and peculiar individuals can be found especially in cities. For example, females might be light due to mutations. Mutations can work in several ways causing changes in pigment production or in its appearance traits. Lightly coloured mallards produce pigments, but their colour appearance has changed. If an individual does not produce melanin pigments at all, it becomes a completely white albino.

Colour variations are thought to be typical in mallards in city environments, where predator pressure is lower and thus exceptional individuals survive better. On the other hand, mallard farming has potentially produced weird-looking individuals that have escaped and spread their genes to natural populations.

These peculiar mallard males in wintering flocks are actually females. The pictures show intersexual females together with two normal males and a female. Moulting males changing their eclipse plumage into nuptial plumage can look similar, but their beak colour once again reveals the actual sex. These pictures were also taken in the middle of winter, when males have already changed to their nuptial plumage.

The beak has an important role in identifying mallard sexes because males have yellow beaks and females have orange-spotted beaks around the year. The beak can also reveal intersexual females. They are individuals that express both female and male outfit. This can be caused by disturbances in female hormone production, or then an individual has both female and male features. Hormones regulate the outfit, and if large quantities of testosterone are produced, male plumage may result. Beak colouration is not as sensitive to hormonal changes and even though a female displays male characteristics, it will still have a female beak.

Hybrid ducks

This common teal x mallard hybrid male was coupled with a normal mallard female and defended it against clearly larger mallard males.

Mallard flocks may also have hybrid individuals. Duck species are close relatives, and can thus mix rather easily. Various species mixes are known, for example mallards can mix with common teals, Eurasian wigeons, northern pintails and black ducks. However, hybrids are quite rare, because each duck species have specific behaviours and characteristics that prevent hybridization. But sometimes these barriers collapse, and hybrid individuals are born. Hybrid individuals express characteristics from both original species. Their habits and characteristics typically do not interest individuals from the original species and therefore might not breed successfully.

Hybridization can cause several problems, which in the worst-case scenario can lead to the extinction of the original species. The hybridizations of mallard and black ducks in North America is becoming more common after shifts in their distribution. Hybridization is now threating black duck populations. Alien mallards can also cause a serious risk for endemic duck species and to their gene pool. For example, the Hawaiian duck (Anas wyvilliana) is unfortunately going extinct because of non-native mallards. Survival of the species now depends on protection actions that target the extirpation of all mallards and hybrids from the islands

Four naturally different mallards wintering in southern Finland. The normal type male was coupled with a normal female. An intersexual and a light female are in the upper part of the picture.

Mallards are commonly farmed, and several different colour variations exist among the domestic breeds. A white duck known by everyone is also a mallard variant. Farmed mallards have sometimes escaped, and now breed with natural mallards. Extraordinary ducks, resembling mallards more or less, are a fairly common sight in Southern and Central European parks. Alien genes in the natural mallard population become more rare in the northern parts of Europe.

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Fish inhabit boreal lakes throughout the year and aquatic invertebrates living in the same lakes belong on the menu of several fish species. Ducks also utilize these same invertebrates for half the year. Even ducks that usually eat plants consume invertebrates; especially females preparing to lay eggs and small ducklings need protein in their diet. Boreal lakes are typically barren and invertebrate-poor. A newly published review article emphasizes the need to carefully deliberate when considering the introduction of fish in wetlands where they do not originally belong or that are established specifically for ducks.

Fish modify the structure of aquatic invertebrate communities, and thus the structure, abundance and diversity of invertebrate communities differ between lakes with and without fish. Fish predate especially large invertebrates that typically are the top predators of invertebrate communities. Therefore the community structure is skewed towards smaller species in lakes with fish.

Invertebrates living among vegetation are better protected from fish predation and thus predation is higher in open water. This means that fish compete especially with those duck species that forage in the open water (e.g. teal), while species foraging among vegetation are less affected (e.g. mallard).

The review article clearly showed that the food competition caused by fish is harmful for breeding ducks. However, the situation is not always clear, because fish and duck abundances are typically limited by the same environmental key factors such as lake productivity. Thus both ducks and fish can be abundant in lakes rich in invertebrate and vegetative food material. But this competitive set-up is emphasized in barren lakes.

Researchers in Finland introduced fish to lakes that had become fishless due to acidification. Monitoring showed that the lake use by common goldeneye broods declined after these introductions. Pairs on the other hand continued using the lakes as before. The difference is suggested to be caused by the foraging manners of ducks at different life stages. Adult ducks find their food from the lake benthos, while ducklings and fish concentrate on competing over nektonic invertebrates. Competition theory is also supported by other studies: ducklings need to use more time foraging in lakes with fish, and still seem to grow slower than in fishless lakes.

The fish experiment was performed in the opposite way in Sweden, where fish were eradicated from certain lakes. Researchers found that all invertebrate groups became more abundant and goldeneye brood numbers increased.

In Finland lakes have been recovering from acidification and this has positively reflected to fish populations. The recovery of fish might affect the breeding success of ducks in boreal lakes, especially concerning breeding goldeneyes.

The competition between fish and ducks is asymmetric in the sense that fish will affect ducks, but ducks do not affect fish. Fish are present in the lakes year-round and if times are thin, the fish just grow slower. They also affect the invertebrate populations of lakes. Ducklings will also grow slower in bad times, but their mortality increases rapidly if food becomes scarce. The effect of ducks on invertebrates is also milder. Thus fish should not be introduced to wetlands established especially for ducks.